Conventional lawn and garden tractor vehicles are well adapted for use as mowing vehicles. They typically include four ground engaging wheels, the rear pair of wheels being driven and the front pair of wheels being pivotable to steer the vehicle. Conventional lawn tractors include an engine mounted at the front of the vehicle. An operator station includes a seat upon which the operator sits behind the engine. Conventional lawn tractors such as these having front mounted engines are well accepted by residential consumers. These vehicles are quite maneuverable and therefore perform well mowing grassy areas such as residential lawns. The steerable front wheels allow the vehicle to execute relatively sharp turns of relatively small radius, but generally do not allow zero radius turns or spin turns. In a zero radius turn a vehicle executes a turn about a vertical axis passing through one of its rear driven wheels. In a spin turn a vehicle executes a turn about a vertical axis passing through the centerline of the vehicle. Conventional lawn tractors have the disadvantage of being less maneuverable than vehicles that are capable of executing zero radius turns or spin turns.
It is known to provide mowing vehicles that execute zero radius turns and spin turns. One such type of vehicle provides independently controlled hydrostatic drives which can drive respective left and right drive wheels at different speeds to cause the vehicle to execute a turn to the side of the slower wheel. Left and right control levers extend from the hydrostatic drive mechanisms and can be manipulated by the operator seated in the operator station for controlling the speed of the respective drive wheels. As the operator pivots the right control lever forwardly the hydrostatic drive for the right drive wheel causes the right drive wheel to rotate in a forward direction. The farther the operator pivots the lever forwardly the faster the drive wheel will rotate. If the operator pivots the right control lever rearwardly, the right drive wheel will be driven in reverse. The farther the operator pivots the lever rearwardly, the faster the right drive wheel will rotate in reverse. The left drive wheel operates in similar fashion in response to the operator manipulating the left control lever. When the operator pivots both levers forwardly the same amount, both drive wheels rotate forwardly at the same speed and the vehicle is propelled forwardly in generally a straight line. To execute a turn during forward travel the operator can pivot one lever rearwardly with respect to the other lever to execute a turn in that direction. For example, with both levers pressed forward to the same degree for straight forward travel, the operator can pull back the left control lever slightly with respect to the right control lever, which will slow the left drive wheel relative to the right drive wheel, and therefore the vehicle will execute a turn to the left.
When the vehicle is stationary, the operator can pivot one control lever forwardly while keeping the other in its upright neutral position. This will cause one drive wheel to be driven forwardly while the other drive wheel remains stationary, and therefore the vehicle will execute a zero radius turn, which is a turn about a vertical axis passing through the stationary drive wheel.
The operator of such a vehicle can also execute a spin turn by pivoting one control lever forwardly and the other control lever rearwardly. This causes one drive wheel to be driven forwardly and the other drive wheel to be driven in reverse, which causes the vehicle to pivot or turn about a vertical axis located somewhere between the two drive wheels. If both drive wheels are rotating at equal and opposite directions, then the vehicle will execute a spin turn about a vertical axis positioned on the centerline of the vehicle equidistant between the two drive wheels.
Conventional lawn mowers of this type have the advantage of being highly maneuverable. They can execute zero radius turns or spin turns. This tight turning is particularly advantageous when an operator comes to an end of a yard during mowing operations and wants to turn around and mow in the opposite direction. The operator can simply execute a zero radius turn and begin mowing back in the opposite direction. Furthermore, spin turns are advantageous when mowing in tight spaces or when maneuvering out of confined spaces such as a storage garage. The vehicle can be driven straight into a storage building, and then when it is time to drive out of the building the operator can execute a spin turn and drive forward out of the building.
Conventional lawn mowers of this type having independently controlled hydrostatic transmissions for each drive wheel can be relatively difficult for some people to operate. The left and right control levers can be somewhat difficult for first time operators to become comfortable using. Making an accurate turn during mowing operations alongside structures such as flower beds can be difficult for many operators using the left and right hand control system. Since the controls are so different from conventional steering and foot pedals such as are found in automobiles, many customers of mower vehicles will not choose to purchase a vehicle having left and right control levers such as the typical zero turning radius mower. Because of leakage and other small differences in the two hydrostatic transmissions on each vehicle, the operator may have to hold the left and right control levers at slightly different forward positions to drive the vehicle in a straight line, and therefore it may be difficult for an operator to drive the vehicle in a straight line using the control levers. If the operator can not locate the proper locations the levers must assume in order to travel forward in a straight line, the operator will have to constantly make corrections and steer the vehicle back to the intended path of travel.
Conventional zero turning radius mowers position the engine to the rear of or directly over the rear drive wheels, and therefore there is no large amount of weight carried far in front of or behind the rear drive wheels that has to be swung about during a turn. The position of the engine over the rear drive wheels of conventional zero turn radius mowers also helps place a large portion of the vehicle weight on the drive wheels, which will increase traction at the drive wheels and thereby enhance the vehicle""s ability to execute turns.
Typical dual hydrostatic zero turning radius mowers have a mower deck that is mounted in front of the vehicle or between the front and rear pairs of wheels. The engine is mounted to the rear of the vehicle, and the operator station and seat are positioned generally in front of the engine. Because of its configuration, this type of vehicle can be perceived by the average consumer to be quite different from a conventional lawn tractor having its engine mounted at the front of the vehicle and the mower deck mounted between the front and rear pairs of wheels. Therefore, some consumers might not purchase one of these dual hydrostatic types of vehicles because it does not meet his expectations of what a lawn mowing vehicle should be.
Another type of transmission allows a vehicle to execute zero radius turns and spin turns. Military tank vehicles and other tracked vehicles have been provided with a dual differential transmission capable of zero radius turns and spin turns. This type of drive and steer transmission is described in the articles entitled Tanks And Dozers Turn On A Dime With New All-Gear Steering, and Tank-Steering Mechanisms. The transmission includes a driving portion having a driving differential which receives rotational power from the vehicle power source for propelling the vehicle during operation. The driving portion includes an drive input control which can be operatively engaged by the operator for varying the speed and forward/reverse direction of the vehicle. The transmission also includes a steering portion having a steering differential. The steering portion includes a steering input control that can be operatively engaged by the operator for executing turns. The steering portion engages the driving portion such that as the steering input control is engaged by the operator to execute a turn the steering portion increases the speed of the track on one side of the vehicle and proportionately decreases the speed of the track on the other side of the vehicle. In this manner the vehicle executes a turn. When the vehicle is stationary, the operator can engage the steering input control, which will cause the tracks on one side of the vehicle to be driven forwardly, and the tracks on the other side of the vehicle to be driven rearwardly at the corresponding speed. This causes the vehicle to execute a spin turn.
As described in the article entitled Tank-Steering Mechanisms, a different transmission having planetary gear arrangements functions in a manner similar to the dual differential drive and steer transmission described above. This type of transmission also includes a driving portion having a driving input control, and a steering portion having a steering input control. The steering portion interacts with the driving portion to increase the speed of the tracks on one side of the vehicle and correspondingly decrease the speed of the tracks on the other side of the vehicle.
These types of drive and steer transmissions allow the vehicle to be highly maneuverable, and allow the vehicle to execute zero radius turns and spin turns. These drive and steer transmissions are typically provided on heavy duty vehicles such as military tanks, bulldozers, and other large tracked vehicles.
It would be desirable to provide a front engine lawn tractor that has improved maneuverability so that the vehicle can execute tighter turns and more easily operate in confined spaces. It would be desirable for such a vehicle to have the characteristics of a front engine lawn tractor such that the vehicle will meet residential consumers""expectations of a lawn mower vehicle. If such a vehicle is a front engine type vehicle, parts and manufacturing methods could be used that are common with conventional front engine lawn tractors, which would reduce the cost of manufacturing such a vehicle. It would be desirable for such a vehicle to have automotive type controls that most consumers are familiar and comfortable with.
The preferred embodiment of the present invention provides a riding lawn tractor having an operator station whereat the operator sits during mowing operations. An engine is mounted to the vehicle frame in front of the operator station. The lawn tractor includes a drive and steer type transmission which powers the rear drive wheels for propelling the lawn tractor across the ground. The drive and steer transmission serves to drive the rear wheels at different speeds when the operator turns a steering wheel in the operator station to thereby execute a vehicle turn. The various vehicle components are located on the vehicle to establish an optimum weight distribution between the front and rear pairs of wheels. The engine is positioned slightly to the rear of where an engine is supported by most convention lawn tractors. More of the engine""s weight is therefore transmitted to the rear wheels. The battery can be carried behind the axis of the rear drive wheels such that its weight is borne by the rear wheels. The gas tank is positioned at the rear of the vehicle and behind the axis of the rear wheels such that the weight of the gas tank and gas is transmitted to the rear ground wheels and not the front wheels. The operators seat is adjustable fore and aft to a variety of different positions. The seat""s range of motion is located such that the seated operator""s center of gravity is located above or behind the axis of the rear wheels when the seat is adjusted to its rearward most or intermediate positions. Only when the seat is adjusted to its forward most positions is the center of gravity of the seated operator in front of the axis of the rear wheels. When larger operators use the vehicle, they will tend to shift the seat to the rear, which positions their center of gravity to the rear of the axis of the rear wheels and transmits their weight to the rear wheels. Only the smallest operators, who are presumably relatively light, will position the seat in its forward most positions. The relatively small weight of these smaller operators will have a relatively small impact on the amount of weight borne by the front wheels and will not significantly affect the distribution of weight between the front and rear pairs of wheels.
The location of the vehicle components as described above results in an optimum weight distribution between the front and rear pairs of wheels which allows a drive and steer type of transmission to be utilized with a front engine lawn tractor. Approximately seventy-five percent of the operator and vehicle weight is borne by the rear wheels, which is sufficient to establish good traction between the rear drive wheels and the ground surface for driving and steering the vehicle. Approximately twenty-five percent of the operator and vehicle weight is borne by the front wheels, which is sufficiently large to hinder the vehicle from tipping rearwardly about the rear wheels such as when traveling up a slope, yet is sufficiently small to allow the front end of the lawn tractor to be easily swung around by the rear drive wheels to execute a turn.
The present invention therefore provides an arrangement of vehicle components that establishes a weight distribution between the front and rear wheels of a lawn tractor that allows the effective use of a drive and steer type of transmission with a front mounted engine type lawn tractor. The drive and steer type transmission improves the maneuverability of the front engine lawn tractor so that the vehicle can execute tighter turns and more easily operate in confined spaces. The vehicle according to the present invention has the characteristics of a front engine lawn tractor such that the vehicle will meet many residential consumers""expectations of a lawn mower vehicle. Parts and manufacturing methods can be used on the lawn tractor according to the present invention that are common with conventional front engine lawn tractors, which will reduce the cost of manufacturing such a vehicle. The vehicle according to the present invention provides automotive type controls that most consumers are familiar and comfortable with.